On Tue, Dec 04, 2018 at 09:38:29AM -0800, Sagi Grimberg wrote: > > > > > Yes, I'm very much in favour of this, too. > > > > We always have this IMO slightly weird notion of stopping the queue, set > > > > some error flags in the driver, then _restarting_ the queue, just so > > > > that the driver then sees the error flag and terminates the requests. > > > > Which I always found quite counter-intuitive. > > > > > > What about requests that come in after the iteration runs? how are those > > > terminated? > > > > If we've reached a dead state, I think you'd want to start a queue freeze > > before running the terminating iterator. > > Its not necessarily dead, in fabrics we need to handle disconnections > that last for a while before we are able to reconnect (for a variety of > reasons) and we need a way to fail I/O for failover (or requeue, or > block its up to the upper layer). Its less of a "last resort" action > like in the pci case. > > Does this guarantee that after freeze+iter we won't get queued with any > other request? If not then we still need to unfreeze and fail at > queue_rq.
It sounds like there are different scenarios to consider. For the dead controller, we call blk_cleanup_queue() at the end which ends callers who blocked on entering. If you're doing a failover, you'd replace the freeze with a current path update in order to prevent new requests from entering. In either case, you don't need checks in queue_rq. The queue_rq check is redundant with the quiesce state that blk-mq already provides. Once quiesced, the proposed iterator can handle the final termination of the request, perform failover, or some other lld specific action depending on your situation.
